good or bad?

Can anyone Id this odd looking thing? At first I thought maybe a sponge but not so much now

Can someone help indentify the item I circled in yellow? It has grown from nothing to this within about 10 days. It is super hard like a shell and I cannot get if off the rock with normal tweezers. I would have to use more force I think. (Don't want to bother it further until I know if it is...

Hello - I have had my 1500 Cade setup since December and to be honest, I am struggling. I have had some livestock die for no reason, but for the most part, all of my fish are thriving. My corals are touch and go - some of the harder ones to keep are growing strong and some of the easier ones...

One last question. I had a couple of things growing on my euphyllia coral stems. Also some fishing line sized worm looking pests on my live rock that I took a polyp off of. Are these pests to be worried about? Thoughts? I really need some input, thanks!